The present disclosure relates generally to controlling the operating pressures within subterranean boreholes, and in particular, to a controller apparatus, system and/or method for controlling the operating pressures using a choke piston controller with a mechanical linkage in a fluid control system.
Many applications involve control of the back pressure of a fluid flowing in a system. For example, in the drilling of oil wells, a drill pipe is typically suspended in the wellbore with a bit on the lower end thereof. As the bit is rotated, a drilling fluid, such as a drilling mud, is circulated in a downward direction through the interior of the drill string and through the bit. The drilling fluid is circulated from the annulus of the wellbore to the surface. This fluid circulation is maintained for the purpose of removing cuttings from the wellbore, for cooling the bit, and for maintaining hydrostatic pressure in the wellbore to control formation gases and prevent blowouts, and the like. In those cases where the weight of the drilling mud is not sufficient to contain the bottom hole pressure in the well, application of additional back pressure on the drilling mud at the surface is conducted to compensate for the lack of hydrostatic head to keep the well under control. Thus, in some instances, a back pressure control device is mounted in the return flow line for the drilling fluid. Back pressure control devices are also used for controlling “kicks” in the system caused by the intrusion of salt water or formation gases into the drilling fluid which may lead to a blowout condition.
For example, U.S. Pat. Publ. 2008/0149182 A1, assigned to the assignee of the present application and incorporated herein by reference in its entirety, discloses a linear motor which drives a hydraulic system to control a choke to provide a pressure balancing force. A typical well for drilling for oil and/or gas is also disclosed. To control the operating pressures within the well within acceptable ranges, a choke is used to bleed pressurized fluidic materials from an annulus into a mud tank in a controlled manner to thereby create back pressure within the wellbore. The choke, in some well systems, is manually controlled by a human operator to maintain certain operating pressures within the well within acceptable ranges. The operator manually maintains the operating pressures within predetermined acceptable limits by manually adjusting the choke.
Moreover, maintenance of an optimum back pressure on the drilling fluid is complicated by variations in certain characteristics of the drilling fluid as the drilling fluid passes through the back pressure control device. For example, the density of the fluid is altered by the introduction of debris or formation gases, and/or the temperature and volume of the fluid entering the control device changes. Therefore, the desired back pressure is not achieved until appropriate changes have been made in the throttling of the drilling fluid in response to these changed conditions.